Allisartan isoproxil (CAS: 947331-05-7), with the chemical name: 2-butyl-4-chloro-1-[2′-(1H-tetrazol-5-yl)-1, 1′-biphenyl-methyl]-imidazole-5-carboxylic acid, 1-[(isopropoxy)-carbonyloxy]methyl ester, and the brand name: Xinlitan, is a new-type angiotensin II receptor antagonist. Chinese patent CN200610023991.0 firstly discloses its chemical structure and its application in the preparation of antihypertensive compositions. Compared with other antihypertensive products (such as losartan) of the same type, allisartan isoproxil shows advantages, such as low toxicity and excellent antihypertensive effect.

Study on polymorphism of drugs for superior polymorph is an important part in the process of drug research and also one of the important technologic steps for drug quality control. According to statistics, the vast majority of drugs are polymorphism, which directly affects the physicochemical properties (such as melting point, solubility, dissolution and stability) and clinical efficacy. Because specific polymorph is very unpredictable to be obtained, the physicochemical properties for different polymorphs of the same active ingredient are difficult to be predicted.
Chinese patent CN200710094131.0 discloses an allisartan isoproxil polymorph and its preparation method. This allisartan isoproxil polymorph is characterized by high stability, but with electrostatic phenomenon and poor flowability, even worse after grinding, easy to generate dust in the production process which causes contamination and also influences the feeding and blending in the following production process.
Chinese patents CN200710094021.4 and CN201110289695.6 separately disclose different preparation methods of allisartan isoproxil, the inventor repeats and finds that the polymorph of allisartan isoproxil obtained are consistent with that disclosed in Chinese patent CN200710094131.0.
In order to solve the shortcomings of available technologies, the inventor firstly tries to find a way to get an allisartan isoproxil crystal with non-electrostatic phenomenon, good flowability and high stability. By further research on the obtained crystal, the inventor is surprised to find that the obtained allisartan isoproxil crystal is a polymorph has not been disclosed, shows high stability, and meets the requirements of subsequent production. The new polymorph provides more options in raw materials for allisartan isoproxil preparation.